Conventional anaerobic digesters include plug-flow digesters, lagoon-type digesters, and batch digesters. A conventional plug-flow digester is described in U.S. Pat. No. 6,673,243 to Srinivasan et al., the disclosure of which is incorporated herein by reference. This plug flow digester comprises a reactor divided into a number of connected chambers that retain fluid and manure/compost slurry. The digester of the '243 patent utilizes a continuous fermentation in a single, large batch size. The flow of waste (i.e., the chamber segments each containing manure/organic waste slurry) is directed through the digester to ensure that the waste passes through each chamber before exiting the digester.
The single, large batch size of the '243 patent is disadvantageous because the slurry can sit still for lengths of time, flow passages can become clogged, production of biogas can take longer, and the operator has no control over the temperature of the digestor or the amount of time that the slurry remains in each chamber segment. Thus the system of the '243 patent can be unpredictable.
Some conventional digesters also include moving parts (e.g., and auger or other mixing device) that must be powered. Such a design thus uses more energy to create the biogas, resulting in a less energy-efficient system. The moving parts can also lead to undesirable breakdowns and associated repair time and expenses. Also, some conventional digesters do not operate well in cold temperatures.
Therefore it may be desirable to provide an inexpensive and easy-to-build compartmentalized anaerobic digester that gives an operator more control of the digestate through temperature and pH adjustment. Such control may be achieved by adjusting speed of movement of the slurry/digestate through the digestor, thereby varying the length of digestion time. Control of the digestion process can also be achieved by smaller batches/segments within the compartmentalized chamber.